21216061 has 2 divisors, whose sum is σ = 21216062. Its totient is φ = 21216060.

The previous prime is 21216053. The next prime is 21216073. The reversal of 21216061 is 16061212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20304036 + 912025 = 4506^2 + 955^2 .

It is a cyclic number.

It is not a de Polignac number, because 21216061 - 2³ = 21216053 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21216001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608030 + 10608031.

It is an arithmetic number, because the mean of its divisors is an integer number (10608031).

Almost surely, 2^21216061 is an apocalyptic number.

It is an amenable number.

21216061 is a deficient number, since it is larger than the sum of its proper divisors (1).

21216061 is an equidigital number, since it uses as much as digits as its factorization.

21216061 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21216061 is about 4606.0895562288. The cubic root of 21216061 is about 276.8353750786.

Adding to 21216061 its reverse (16061212), we get a palindrome (37277273).

The spelling of 21216061 in words is "twenty-one million, two hundred sixteen thousand, sixty-one".